1. Field of the Invention
This invention relates generally to the field of encasement or encapsulation of structural members and more particularly to a polymer encapsulation for repair or protection of such structural members.
2. Background Art
The use of piles or piers as structural supports for wharfs, bridges or other marine environment structures is well known. The usual materials of construction for such marine structures are concrete, steel, wood or a combination or composite of two or more of these materials. All three of these materials of construction are vulnerable to corrosion or deterioration above, at or below the water line. Such support piles may be damaged or subject to deterioration by salt water, corrosive pollution, cycles of wetting and drying, cycles of freezing and thawing and electrolysis. Erosion, marine organisms, mechanical impact, water content and abrasion may also cause premature failures of even properly designed structures.
Protecting piles, risers, piers, supports, columns or other load supporting structural members used in a marine environment is often times unreliable and time consuming. Some alternatives or methods for arresting deterioration in marine support structures such as vinyl wraps, protective coatings, and concrete encasements have been tried, but with inconsistent results. These means of repair or protection are only short term solutions and may be unfeasible for certain structures. For instance, vinyl wraps are subject to puncture and tearing from mechanical impact. Most protective coatings eventually fail due to inadequate surface preparation, improper application, ultra violet light exposure, mechanical wear or pinhole defects. Concrete encasements used as repairs and protective encapsulation are often unsuitable as they result in too heavy an additional load for the structure to support and the porous encapsulation may be subject to penetration by chlorides and marine organisms.
A known repair and protective procedure for damaged, as well as new piers or piles, provides for encapsulation in a corrosion resistant polymer jacket. By pouring a flowable mixed epoxy material into a surrounding form or jacket, the epoxy grout would solidify or harden about the pile, thus sealing off oxygen and preventing corrosion as well as structurally repairing the pile. For an example of such protective and repair encapsulation see U.S. Pat. No. 4,019,301 to Fox and the references cited therein which are hereby all fully incorporated herein by this reference. While an improvement over prior practice, the Fox method can often be unreliable. By simply pouring the batch mixed epoxy encapsulating material into the surrounding form, no assurance is obtained that gravity flow will effect elimination of voids or seams by completely filling the surrounding form or that premature set up of the encapsulating material will not channel the filling material flow. Through the process of pouring the epoxy into the submerged fiberglass jacket or form, water can dilute, entrain or mix with the epoxy, thus adversely affecting the engineering properties of the protective or repair system. The pouring procedure also can create holidays or non-bonded cold joints between pours, be very time consuming, messy and impractical for structures that are not readily accessible. Furthermore, no provision was made for verifying, by visual observation or otherwise, that the encapsulating material fully filled the jacket form or for field verifying that adequate structural bonding to the structure has occurred.
Pumps have been developed to place mixed or catalyzed epoxy encapsulating material in the surrounding jacket. This method offered a substantial improvement over batch pouring, but still presented a problem due to the gravity driven flow of the catalyzed epoxy grout used to fill the jacket or form and the catalyzed epoxy grout setting up prematurely in hoses and equipment. Also, the end product properties are highly dependant upon proper mixing of each batch by personnel in the field. If inexperienced personnel are used, inconsistent batches of epoxy are often the result.
The repair and protective encapsulation process was normally accomplished by installing a custom built prefabricated jacket about the piling to form the continuous annular void. After a lower seal for the grout filling was effected between pile and jacket, the two-component polymer was then mixed and poured or pumped into the top of the void for filling and curing in place. As a polymer grout has a limited "pot life" or working time after mixing with the catalyst, any unanticipated delay would result in loss of the mixed polymer from undesired hardening or a serious deterioration in quality. Premature setting or solidifying of the polymer grout, usually an epoxy based resin, could also result in lost time for cleaning as well as requiring hose and equipment replacement. Because of this limited "pot life", encapsulation was essentially an individual or "batch operation". While this is acceptable if only a few piles are to be repaired or protected, it is much too costly and unreliable for entire structures, such as a wharf or a causeway, which may have hundreds of piles.
The batch processing and pouring had a severe additional limitation as the bond strength between the encapsulating material and the load supporting or structural member, to form a unitary structure, was usually inconsistent. This drawback was magnified by the unavailability of a suitable, simple field test or instrument to measure or verify this vital property or characteristic.